BUG=chromium:721078,v8:6246

Change-Id: I10f20d9cc2c7cabff8a3fba02aff351fcecc0ce2
Reviewed-on: https://chromium-review.googlesource.com/505611Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Mythri Alle <mythria@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45304}